Merge pull request #207 from gvergnaud/gvergnaud/fix-exhaustive-match…

…ing-on-readonly-arrays

fix(readonly): exhaustive matching on readonly array

package.json

@@ -1,6 +1,6 @@
 {
   "name": "ts-pattern",
-  "version": "5.0.5",
+  "version": "5.0.6",
   "description": " The exhaustive Pattern Matching library for TypeScript.",
   "type": "module",
   "source": "src/index.ts",

src/types/ExtractPreciseValue.ts

@@ -20,8 +20,6 @@ export type ExtractPreciseValue<a, b> = b extends Override<infer b1>
   : // inlining IsAny for perf
   0 extends 1 & a
   ? b
-  : b extends readonly []
-  ? []
   : b extends readonly any[]
   ? ExtractPreciseArrayValue<a, b, IsReadonlyArray<a>>
   : b extends Map<infer bk, infer bv>

src/types/Match.ts

@@ -34,8 +34,7 @@ export type Match<
   with<
     const p extends Pattern<i>,
     c,
-    value extends MatchedValue<i, InvertPattern<p, i>>,
-    excluded = InvertPatternForExclude<p, value>
+    value extends MatchedValue<i, InvertPattern<p, i>>
   >(
     pattern: IsNever<p> extends true
       ? /**
@@ -52,12 +51,14 @@ export type Match<
       selections: FindSelected<value, p>,
       value: value
     ) => PickReturnValue<o, c>
-  ): Match<
-    Exclude<i, excluded>,
-    o,
-    [...handledCases, excluded],
-    Union<inferredOutput, c>
-  >;
+  ): InvertPatternForExclude<p, value> extends infer excluded
+    ? Match<
+        Exclude<i, excluded>,
+        o,
+        [...handledCases, excluded],
+        Union<inferredOutput, c>
+      >
+    : never;
 
   with<
     const p1 extends Pattern<i>,

tests/readonly.test.ts

@@ -1,4 +1,4 @@
-import { match } from '../src';
+import { P, match } from '../src';
 import { Equal, Expect } from '../src/types/helpers';
 
 describe('readonly', () => {
@@ -71,5 +71,16 @@ describe('readonly', () => {
           })
           .exhaustive();
     });
+
+    it('must support exhaustive matching on readonly arrays', () => {
+      const sum = (xs: readonly number[]): number =>
+        match(xs)
+          .with([], (x) => {
+            type t = Expect<Equal<typeof x, readonly []>>;
+            return 0;
+          })
+          .with([P._, ...P.array()], ([x, ...xs]) => x + sum(xs))
+          .exhaustive();
+    });
   });
 });